The problem faced by a roaming mobile terminal user is firstly to be able to connect to a network to access the various voice, messages, data services, etc., and secondly when the supply host network becomes plural, to optimize the selection of a network.
It is appropriate here to distinguish a host network to which a user has a right of access, for example through a subscription for its mobile terminal, from a visited network. The right of access is materialized, for example, by a SIM card, and especially by an IMSI code that uniquely identifies said mobile terminal to the host network.
In his/her of usual circulation area, the user connects his/her mobile terminal to a regular host network via at least one cell of said host network located within the range thereof. However when travelling, roaming away from said host network range, this is no longer possible. Instead when roaming, the user connects his/her mobile terminal via a cell within range, with said cell belonging to a visited network.
The operators of the different networks which operate, as appropriate, as host or visited network, enter in reciprocal agreements and roaming agreements, in particular according to their geographic coverage, thus enabling a user to temporarily “borrow” the means of a visited network to connect, provided an agreement has been signed between said visited network and the host network. The network host manages the billing of services to the user if the latter uses a visited network having a roaming agreement with the host network.
In some applications, the selection of the visited network is arbitrated by a list of ordered preference of networks. This list is managed and updated by the (host) network operator. It is then downloaded to the mobile terminal typically by means of an OTA (Over The Air) protocol. The network regularly queries the mobile terminal for the values of various criteria. Depending on these values, the system updates the preference list and downloads it to the mobile terminal. Such a process requires the exchange of significant volumes of data and high associated costs and, in addition, the duration thereof entails a significant lack of reactivity. Such a process, which can be operated by a list of preferred networks, is by definition, static: switching from one network to another one in the list between two updates is possible only in case of loss of the signal from a network placed higher in the list.
The various networks, sometimes acting as a host network and sometimes as a visited network, negotiate roaming agreements. For a given geographic area, a host network does not necessarily have an agreement with all the networks available in this geographic region and thus does not offer a user an optimal coverage and/or for the best price.
Then a need exists to optimize the selection of the visited network, in order to have the best quality of available network and/or the most advantageous agreements between the operators.